This invention relates to guardrails intended to be positioned along a highway to reduce injury to the driver and passenger of vehicles that may accidentally tend to leave the highway.
In one class of guardrail system, each guardrail system includes an elongated barrier and at least one energy-absorbing terminal. The elongated barrier extends parallel to the roadway along the side of the roadway and ends in a terminal. The terminal cooperates with one or more components of the barrier to absorb energy when a vehicle hits the terminal itself.
The terminal is constructed to stop the vehicle without subjecting the occupant to excessive forces and to avoid impaling the passenger compartment of the vehicle or redirecting the vehicle in a dangerous direction or permitting the vehicle to continue in a dangerous direction at a dangerous speed when the vehicle hits the terminal itself. The barrier is designed to redirect the vehicle in a safer direction and impede its progress when the vehicle hits the barrier itself.
The terminals and barrier of the energy-absorbing guardrail are designed so that:                (1) when the vehicle hits the barrier itself, the barrier is anchored by a cable or similar component with tensile strength to support the vehicle from moving excessively in a direction perpendicular to the roadway; and (2) when the vehicle hits the terminal, the cable or other support member is released to avoid pulling the barrier out of its alignment with the terminal which would prevent the movement of the terminal and barrier together to absorb energy.        
A prior art guardrail of this class is described in U.S. Pat. Nos. 4,928,928 and 5,078,366 filed in the name of Sicking, et al. This prior art energy-absorbing guardrail has a terminal that extrudes a metal portion of the barrier, which is generally a W-beam rail or the like. In this prior art guardrail, the terminal, upon impact by a vehicle, moves along the rail, forcing the rail into a narrowing chute to extrude the rail and bend it into a roll, thus absorbing energy from metal working the rail. When the terminal is impacted, the cable anchoring the rail is released by the force of the impact.
This type of guardrail has several disadvantages, such as for example: (1) it is relatively expensive; and (2) the basic configuration cannot be readily adapted to different thickness of beam or to different materials from which the barrier may be constructed. Moreover, it is difficult to adapt the basic design to absorb energy at different rates depending on the nature of the roadway along which it is positioned. Thus, the rate of absorbing energy is the same for highways adapted to carry trucks and other vehicles at high speeds as it is for roadways having a lower speed limit and being adapted for smaller vehicles traveling at lower speeds although the highway may call for much more energy absorption per linear foot of travel of the vehicle striking the terminal.
Another prior art energy-absorbing guardrail of this class is disclosed in U.S. Pat. No. 4,655,434 to Bronstad and U.S. Pat. No. 4,838,523 to Walter P. Humble, et al. This prior art guardrail includes two parallel rails with horizontal connecting members between them. The terminal, when hit by a vehicle, moves along the guardrail, hitting the horizontal connecting members as it goes and causing the connecting members to move along a line of perforations in the metal rails, absorbing energy from the metal working as it moves.
This type of guardrail has a disadvantage of being expensive and not adapted for different sizes and speeds of automobiles without special design.